1. Field of the Invention
The present invention generally relates to subterranean drilling equipment. More particularly, the present invention relates to a system and method for detecting roller bit wear in a roller-cutter drill whereby the drilling operation can be ceased prior to roller drill bit failure.
2. Description of the Related Art
In rotary-cutter type subterranean drills, rotary drill bits are a commonly used type of drill bit, especially in the oil and gas well drilling industry, because the rotary drill bit offers a satisfactory rate of penetration with a significant operational life in drilling most commonly encountered formations. Roller cutter drill bits include a bit body having a threaded pin at its upper end adapted to be detachably secured to a drill string suspended from a drill rig, and a plurality of depending legs, typically three such legs, at the lower end of the body. The drill bit further includes a plurality of conical roller-cutters having cutting elements thereon, with one roller-cutter on each leg, and each leg typically includes a bearing for rotatably mounting each roller-cutter thereon.
Sealed bearing type roller-cutter bits further have a lubrication system including a reservoir holding a supply of lubricant. A passage in the bit body extends from the reservoir to the bearing to allow flow of lubricant to the bearing. A seal is disposed between the roller cutter and the bearing journal that holds lubricant in the bit. A diaphragm at the reservoir provides pressure compensation between the lubricant and the drilling fluid in the annulus between the bit and the well bore.
In use, roller cutter drill bits are rotated in the well bore on the end of a drill string that applies a relatively high downward force onto the drill bit. As the bits are rotated, the conical roller cutters rotate on the bearing journals thereby bringing the cutting elements on the roller cutters into engagement with the substrate at the bottom of the well bore. The cutting elements drill through the substrate at the well bore bottom by applying high point loads to the substrate to thereby cause the substrate to crack or fracture from the compression. A drilling fluid, commonly called drilling mud, passes under pressure from the surface through the drill string to the drill bit, and is ejected from one or more nozzles adjacent the roller-cutters and the drilling fluid is then forced back up the well bore to the surface.
For cost-effective drilling, a worn drill bit needs to be replaced due to the reduced rate of drilling penetration for the worn bit. At a certain point, the cost of replacing the old drilling bit with a new bit becomes equal to the cost of the drilling inefficiency, or in other words, the cost of the new bit plus the cost of rig time in tripping the drill string in and out of the well bore is less then cost of operating the worn bit. Unfortunately, once a drill bit is positioned in a well bore, gathering reliable information regarding the operating condition, performance and remaining useful life of the drill bit becomes difficult. Typically, the decision by a drilling rig operator to replace a drill bit is a subjective one, based upon experience and general empirical data showing the performance of similar drill bits in drilling similar substrate formations. However, the rig operator""s decision as to when to replace a drill bit is often not the most cost effective because of the many factors affecting drilling performance beyond the condition and performance of the bit itself
In the worst case, the drilling rig operator may unknowingly run the drill bit until failure. Bit failure may also result from an improper application of the bit, such as by excessive weight on the drill bit from the drilling string, excessive rotational speed, and drilling with the wrong type of bit for substrate being drilled, or even from a defect in the drill bit itself. Bit failures typically occur in one of two modes: (1) breakage of the cutting elements, or (2) bearing failure. The first mode of failure is more common, and the second mode is more serious.
In the first mode, pieces of the cutting elements, which are typically either steel teeth or tungsten carbide inserts, are broken from the roller cutters. This breakage does not normally stop the drilling action but it does significantly reduces the rate of drilling penetration, and the broken pieces are mostly carried away from the well bore bottom by the circulating drilling fluid thereby leaving the well bore bottom clean for a replacement bit.
The second mode of failure can occur if the bit is continued to be used with a failed bearing assembly as the assembly will no longer be able to hold the roller cutter on the bearing journal, and consequently, the roller cutter will fall from the bit when the drill string is pulled from the well bore. A lost roller cutter can be retrieved from the well bore bottom only by a time-consuming and expensive xe2x80x9cfishingxe2x80x9d operation in which a special retrieval tool is tipped in and out of the well bore to retrieve the broken cutter and any pieces.
In sealed bearing roller cutter bits, bearing failure is often the result of a seal failure that causes lubricant to flow out of the drill bit and drilling fluid, which contains abrasive particles, to flow into the bearing. Although less common, diaphragm failure has the same result as seal failure. In any event, bearing failure is almost always preceded by, or at least accompanied by, a loss of lubricant.
Numerous bearing failure indicator systems have been proposed for inclusion in drill bits so as to give the drilling rig operator a signal predicting bearing failure. One such system involves measurement and interpretation of certain drilling parameters at the drill rig, such as drill string torque, weight on bit, and rate of penetration, to predict drill bit bearing failure. In practice this system has proved to be unreliable, which is likely due to the large number of variables other than bit performance, such as the type of formation and the pressure and flow rate of the drilling fluid, which affect the drilling parameters measured at the drill rig.
Another system, involves a marker fluid, such as a radioactive material in the bearing lubricant, which is released into the drilling fluid upon bearing failure. The released marker fluid is detected at the drill rig when the drilling fluid is circulated back up to the surface. While this method does detect the loss of lubricant in a sealed bearing drill bit that precedes, or at least accompanies, the failure of the bearings of the bit, and thus is a reliable indication of bit failure, the system has several shortcomings. In addition to the difficulties present in handling radioactive materials, a significant amount of marker fluid must be released into the relatively large volume of drilling fluid or else become so diluted as to be undetectable.
Therefore, it would be advantageous to provide a system and method to reliably detect the wear of a roller bit prior to catastrophic failure of the roller bit with the roller bit, the roller cutters or pieces thereof requiring extrication from the well bore. Such method should be simple in implementation and not require separate elaborate equipment to be used at the drill rig or on the drill bit. It is to the provision of such an improved method for detecting roller bit bearing wear that the present invention is primarily directed.
The present invention is a system and method for detecting the wear of a roller bit bearing on a roller drill bit body. In the system, the roller drill bit body has at least one bearing and a drilling fluid outlet that selectively has drilling fluid flow through it. A roller bit is rotatably attached to the roller drill bit body at the bearing and adjacent the drilling fluid outlet, and the roller bit includes a channel therein. A valve-plug is positioned between the drilling fluid outlet of the roller drill bit body and the channel of the roller bit, and the valve-plug selectively opens the drilling fluid outlet when significant wear of the roller bit is detected.
In one embodiment, the drilling fluid outlet includes a seat, and the valve-plug includes a head and a shaft. The valve-plug head is removably seated in the seat of the drilling fluid outlet of the roller drill bit body and the valve-plug shaft extends into the channel of the roller bit, and thus, uneven rotation or vibration of the roller bit causes the valve-plug shaft to impact the sides of the channel and to unseat the valve-plug head from the drilling fluid outlet thereby causing drilling fluid to flow through the drilling fluid outlet.
The valve-plug can be embodied in any shape, such as with a head and shaft, as a single elongate body, as a generally frustoconical body, or in any other shape as would be suitable to function as a valve-plug as described herein. Moreover, the valve-plug can be comprised of a single uniform solid material, or can be comprised of several different types of materials having different hardness and tensile strength. For example, when the valve-plug is embodied as having a head and shaft, the valve-plug head can be comprised of a different material than the valve-plug shaft, and can include at least a rim comprised of a brittle material.
If the valve-plug is embodied as having a head of a softer material than the valve-plug shaft, uneven rotation or vibration of the roller bit causes the valve-plug shaft to impact the sides of the channel which causes the valve-plug head to deform and unseat from the drilling fluid outlet thereby causing drilling fluid to flow through the drilling fluid outlet indicating a worn roller bit. If the valve-plug is embodied as having a rim of brittle material, uneven rotation or vibration of the roller bit causes the valve-plug shaft to impact the sides of the channel which causes the rim of the valve-plug head to fracture and unseat from the drilling fluid outlet thereby causing drilling fluid to flow through the drilling fluid outlet.
The present invention further provides a method for detecting the wear of a roller bit bearing on a roller drill bit body having at least one bearing and a drilling fluid outlet selectively having drilling fluid flow therethrough, with a roller bit rotatably attached to the roller drill bit body at the bearing and adjacent the drilling fluid outlet, and the roller bit includes a channel therein. The method includes the steps of placing a valve-plug between the roller drill body and roller drill bit such that the valve-plug is removably fitted in the drilling fluid outlet of the roller drill bit body and extending into the channel of the roller bit, rotating the roller bit, removing the valve-plug from the drilling fluid outlet through the valve-plug impacting the sides of the channel, thereby causing drilling fluid to flow through the drilling fluid outlet, and detecting the drop in drilling fluid pressure attributable to drilling fluid flowing through the drilling fluid outlet due to the removal of the valve-plug.
Preferably, the drilling fluid outlet includes a seat, and the valve-plug includes a head and shaft such that the step of placing a valve-plug between the roller drill body and roller drill bit is placing a valve-plug between the roller drill body and roller drill bit such that the valve-plug head is removably seated in the seat of the drilling fluid outlet of the roller drill bit body and the valve-plug shaft extends into the channel of the roller bit, wherein uneven rotation of the roller bit causes the valve-plug shaft to impact the sides of the channel and to unseat the valve-plug head from the drilling fluid outlet. The step of rotating the roller bit is preferably rotating the roller bit wherein the sides of channel do not significantly impact the valve-plug shaft during even rotation of the roller bit, and the step of unseating the valve-plug head is unseating the valve-plug head wherein uneven rotation of the roller bit causes the through the valve-plug shaft impacting the sides of the channel; the impact with the channel sides is sufficient to unseat the valve-plug head from the drilling fluid outlet to thereby cause drilling fluid to flow through the drilling fluid outlet.
If the valve-plug head is comprised of a different material than the valve-plug shaft, the step of unseating the valve-plug head is unseating the valve-plug head through the valve-plug shaft impacting the sides of the channel which causes the valve-plug head to deform and unseat from the drilling fluid outlet thereby causing drilling fluid to flow through the drilling fluid outlet. If the valve-plug head includes at least a rim comprised of a brittle material, the step of unseating the valve-plug head is unseating the valve-plug through the valve-plug shaft impacting the sides of the channel which causes the rim of the valve-plug head to fracture and unseat from the drilling fluid outlet thereby causing drilling fluid to flow through the drilling fluid outlet.
The present invention therefore provides a simple and inexpensive system and method to detect roller bit wear during the drilling operation using a drop in the drilling fluid pressure as an indication of the condition of the roller bit. Upon uneven rotation or vibration in the roller drill bit occurring from wear of the roller bit bearing, the valve-plug is removed from the drilling fluid outlet, which allows drilling fluid to flow through the outlet, in addition to other outlets where drilling fluid normally flows during operation of the roller drill bit. The several embodiments of the valve-plug can be removed from the drilling fluid outlet through many methods, such as simple dislodging or unseating, deformation within the drilling fluid outlet, or fracture of the valve-plug if it is made from or includes a component of a brittle material.
Other objects, features, and advantages of the present invention will become apparent after review of the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and the Claims.